The Sensex and Nifty rise or fall as the prices of their constituent shares change. Their calculation rules determine how much each share contributes: companies with larger adjusted market-cap weights generally have more influence, while free-float adjustments exclude certain holdings that are not treated as readily investable. Earnings news, global cues, interest-rate expectations and investor flows can move share prices, but these forces are not separate inputs in the index formula.
How the Sensex and Nifty turn share prices into index levels
Both benchmarks use capitalization-weighted methods, so a constituent’s influence depends on its price and the number of shares counted under the relevant index rules. In a simplified capitalization-weighted price index, the calculation is:
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Index value = (aggregate adjusted constituent market capitalization ÷ base adjusted market capitalization) × base index value.
The base value and adjustment mechanics are set by the index methodology. The resulting level is a benchmark calculation, not a direct measure of the entire economy.
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Nifty 50 calculation
NSE Indices says the Nifty 50 has used the free-float market-capitalization-weighted method since June 26, 2009. Its calculation tutorial describes the general method as index market capitalization divided by base free-float market capitalization, multiplied by the base index value. The March 2026 NSE Indices equity methodology governs operational details; the simplified formula is not a substitute for those rules.
Free float means the shares considered available for investors to trade under the index rules. NSE Indices’ tutorial identifies promoter, group-company, locked-in and identifiable strategic holdings as non-free-float. Investible Weight Factors (IWFs), which determine the share adjustment, are derived from company shareholding disclosures submitted to exchanges quarterly, according to NSE Indices’ IWF guidance. Thus, the index does not simply count every issued share.
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Sensex calculation
BSE Index Services describes the Sensex as a capitalization-weighted index. Its general index-mathematics formula is:
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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallIndex level = Σ (constituent price × index shares) ÷ divisor.
For a float-adjusted index, index shares are reduced to exclude closely held shares not available to investors. The divisor helps maintain continuity when constituents or index shares change under the applicable rules. For current Sensex-specific selection and review details, consult the relevant BSE methodology rather than assuming every BSE index has identical rules. See the BSE Index Mathematics Methodology.
Why weights matter
If one constituent represents 8% of an index and another represents 1%, a 1% move in the first has roughly eight times the direct effect of a 1% move in the second, all else equal. This is an illustration of capitalization weighting, not a statement of current Sensex or Nifty weights. Actual weights change; use a dated factsheet for them.
What causes the constituent prices to move?
The formula explains how stock-price changes affect an index; it does not identify why a stock moved. Several forces can influence constituent prices, often at the same time:
- Company results and expectations: Earnings releases or changing expectations about future performance can affect share prices. The RBI’s Annual Report 2022–23 described Indian-market responses to positive corporate earnings releases during that period. That is a historical example, not an explanation for every session.
- Domestic and global cues: International developments and shifts in risk appetite can affect Indian shares. The same RBI report discussed Indian-market movements alongside weak global cues and global central-bank tightening in 2022; these are dated examples.
- Institutional flows: Foreign portfolio investor buying or selling can affect demand, but it is only one influence among many. An RBI Bulletin reported net FPI flows in Indian capital markets turning negative in October 2024 amid geopolitical uncertainty, portfolio rebalancing and global developments. That figure describes October 2024, not current flows.
- Rates and macroeconomic expectations: Expected borrowing costs, inflation, growth and currency conditions can change how investors value companies and sectors. These are possible channels, not a quantitative ranking of what drives the indices.
To explain a particular day’s move, identify the trading date and check contemporaneous stock and sector contributions alongside relevant news. The calculation formula alone cannot establish the day’s cause.
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How the Sensex and Nifty differ
| Point of comparison | Sensex | Nifty 50 |
|---|---|---|
| Administrator | BSE Index Services | NSE Indices |
| Market association | BSE benchmark | NSE Indices benchmark |
| Constituents and selection | Uses its own index universe and rules; check the current methodology and constituent list. | Uses its own index universe and rules; check the current methodology and constituent list. |
| Weighting mechanics | Capitalization-weighted, with float adjustment as applicable under the methodology. | Free-float market-capitalization weighted; NSE Indices says this method has applied since June 26, 2009. |
| Return basis | The return-variant convention used by a particular display or product is not established here; check its documentation. | NSE Indices distinguishes the Nifty 50 price index from Nifty 50 Total Returns, which includes reinvested dividends. |
When comparing an index with a fund or portfolio, match the return basis: a price index and a total-return index are not equivalent because total return includes dividends. Constituent lists, weights and index levels also change, so date any figures you cite.
What a Nifty 50 coverage figure does—and does not—tell you
NSE Indices reported that the Nifty 50 represented 53.73% of the free-float market capitalization of NSE-listed stocks as of March 30, 2026. This is a dated market-coverage statistic, not a current-day reading or the weight of any one constituent. The official Nifty 50 page provides the index information.
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Official methodology and reference pages
- NSE Indices: Calculation of indices
- NSE Indices: Equity Indices methodology, March 2026
- NSE Indices: Investible Weight Factors
- NSE Indices: FAQs
- BSE Index Services: Index Mathematics Methodology
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